I'm getting two errors when testing the redesigned announcements. "Disable comments on announcements" is checked in the course settings, and I set this test announcement up originally with an "available from" date and saved it. 

The orange error appeared immediately when I first opened the announcement and hit "Edit". I'm not sure why this is showing up, because there's no replies allowed with my announcements and it's a test course (so no student access, period).

The red error only appeared when I removed the "available from" date, hit "Save," and then clicked the pop-up's "Send" button. I think it's very common for instructors to begin an announcement for the week, slap an "available from" on it far in the future, edit it a few times as things come up throughout the week, and then remove the delay date to release it immediately.